1. Field of the Invention
The present invention generally relates to a convergence correction device for use with a cathode-ray tube apparatus and the like and a cathode-ray tube using such convergence correction device. More particularly, this invention relates to a convergence correction device using a modulation coil in which a core having wound thereat a coil to which a vertical deflection current is applied is used while the core is being saturated and in which the core around which the coil is wound is made of a material in which a changed amount of a reactance per deflection velocity becomes less than a predetermined value so that a convergence pattern, which is difficult to correct at the intermediate portions of upper and lower separated screens of a cathode-ray tube (hereinafter simply referred to as xe2x80x9cintermediate portionsxe2x80x9d) according to the related art, may be corrected satisfactorily.
2. Description of the Related Art
A convergence characteristic is known as one of important characteristics of a deflection yoke. As a deflection angle of a cathode-ray tube increases and a thickness of a screen of a cathode-ray tube decreases recently, the adjustment of convergence becomes very difficult. In such a case, there are employed convergence correction coils. A modulation coil which applies a saturable-core reactor is available as one of the above-mentioned convergence correction coils. A horizontal deflection current and a vertical deflection current are applied to this modulation coil.
However, when the saturable core having wound thereat the coil to which the vertical deflection current is applied is used while the saturable core is being saturated, there arises a risk that a phenomenon in which bright and dark stripes are produced on the screen of a cathode-ray tube as shown in FIG. 1 will occur. This phenomenon occurs in the saturable core having the characteristic in which the reactance of the saturable core is fluctuated suddenly in a period during which the saturable core is switched from the unsaturated area to the saturated area. This phenomenon occurs such that, when the reactance of the saturable core is fluctuated suddenly, the velocity modulation of the vertical deflection current occurs, thereby resulting in the sweep being fluctuated. Since the reactance value of the core is influenced by a value of a frequency of a current, the above-mentioned phenomenon becomes remarkable in a television set in which a vertical deflection frequency is twice the ordinary vertical deflection frequency (100 Hz).
It is an object of the present invention to provide a convergence correction device in which a core having wound thereat a coil to which a vertical deflection current is applied is used while the core is being saturated and in which the core around which the vertical correction coil is wound is made of a material having a characteristic in which a changed amount of a reactance per deflection velocity becomes less than a predetermined value so that a convergence pattern, which is difficult to correct at the intermediate portions according to the related art, may be corrected satisfactorily.
According to an aspect of the present invention, there is provided a convergence correction device which is comprised of a first core around which a first coil connected to a vertical deflection coil in series is wound, a pair of second cores disposed on one end of the first core and around which a second coil connected to an upper horizontal deflection coil in series is wound, a pair of third cores disposed on the other end of the first core and around which a third coil connected to a lower horizontal deflection coil in series is wound, and a pair of magnets for respectively applying magnetic biases to the second and third cores, wherein the first core is used while it is being saturated so that an amount of magnetic flux generated in the first coil may not increase from a middle stage of a vertical deflection current and the first core is made of a material having a characteristic in which a changed amount of a reactance per deflection velocity becomes less than a predetermined value in which a vertical deflection current may not be suddenly changed by transient phenomena.
According to another aspect of the present invention, a cathode-ray tube of the present invention includes the convergence correction device which has the above-mentioned arrangement and the above-mentioned actions. Then, the first core is used while it is being saturated so that an amount of magnetic flux generated in the first coil may not increase from the middle stage (i.e. intermediate portions) of the vertical deflection position on the screen of a cathode-ray tube and the first core is made of a material having a characteristic in which a changed amount of a reactance per deflection velocity becomes less than a predetermined value in which a vertical deflection current may not be suddenly changed by transient phenomena.
According to the present invention, the convergence pattern, which becomes difficult to correct at the intermediate portions as the deflection angle of the cathode-ray tube increases and the thickness of the screen of the cathode-ray tube decreases, may be satisfactorily corrected without producing bright and dark stripes on the screen.